Hi @Almo, welcome.
There is no need to run the node 24/7 in order to stake.
Coin age will be accumulated whether your wallet in online or offline.
Now, if you only run your wallet part-time, you will probably get a higher number of stakes each time when you online your wallet (you have more coin-age). And the frequency will fall back to a more normalised number the longer you have your wallet running (as your coin-age is consumed).
So, to explain in a different way,
Someone who runs their wallet 24/7 will have a steady frequency of stakes.
Someone who only puts their wallet online sometimes, will be able to stake during that period of being online and probably get a higher stake amount. These amounts will become smaller as coin age reduces.
BTW, you are not gaming the system in this way, if you look at your stake rewards over a longer period of time them amounts gained would be within the 5% inflation
To add, the main reason to run 24/7 would be to act as a full note and support the network